Aspiration Catheter Having Variable Volume Distal Suction Chamber

ABSTRACT

An aspiration catheter is provided in which rapid withdrawal of a piston disposed within a distal region of a catheter lumen creates a sudden pressure drop for ingestion of intravascular matter into the catheter lumen through a distal port while avoiding large losses of suction common with catheters having long aspiration lumens. Conventional aspiration using the same catheter can subsequently complement the procedure by fully removing the ingested matter from the catheter.

FIELD OF THE INVENTION

The invention relates to aspiration catheters for removal from a bloodvessel of thrombotic, atherosclerotic or particulate matter, whether itis adherent to the wall of the blood vessel or suspended in the blood.

BACKGROUND OF THE INVENTION

Aspiration catheters are used commonly in connection with interventionalvascular procedures such as angioplasty, atherectomy, stent placement,and the like to aspirate debris that may result from an interventionalprocedure. They also are useful in removing thrombus (clot masses) thatmay be present in a blood vessel before the interventionalcatheterization procedure is initiated and also are used to remove clotswhether or not other intravascular procedures are intended or have beenperformed. Such procedures are referred to as aspiration thrombectomy oraspiration embolectomy. The existence of such thrombotic material in thevessel may present significant medical risk if the clot migratesdownstream with the blood flow. Thrombus may also form on the luminalwall of the vessel and cause a clinically significant, even a totalocclusion. The different types of material that are aspirated bycatheters will be variously referred to hereinafter as clot orintravascular material or intravascular matter.

The aspiration catheter must be of a length sufficient to reach thetargeted region of the intravascular site from the location ofpercutaneous entry into the vascular system. For coronary proceduresusing percutaneous entry in the region of the groin to access thefemoral artery, the length of the catheter is typically of the order of160 centimeters. If it is determined that aspiration should be performedbefore an interventional procedure the distal end of the catheter isnavigated to the region of intended aspiration, for example, to thelocation where an intravascular blood clot has been determined to exist.With the distal end of the catheter in position, suction is applied atthe proximal end of the catheter to engage the clot by suction to drawthe clot into the distal end of the aspiration catheter. The termssuction, vacuum, partial vacuum, reduced pressure and negative pressureare all used interchangeably in the field of medical devices. Typically,the reduced pressure in the aspiration lumen of the catheter is causedby connecting a syringe to the aspiration lumen at the proximal end ofthe catheter and then retracting the plunger in the barrel of thesyringe to build up negative pressure in the aspiration lumen over thelength of the catheter.

Among the difficulties that may be encountered in the use of anaspiration catheter is that the amount of suction developed at thedistal tip is diminished from that applied at the proximal end of theaspiration lumen as a result of fluid resistance associated with fluidflow through the length of the catheter. The loss of suction may beespecially problematic when trying to dislodge and aspirateintravascular material such as a blood clot, particularly a mature clotthat has adhered to the inner vascular wall and may resist aspiration.

It would be desirable to provide an aspiration catheter that overcomesthe inherent loss of suction over the length of the catheter such that agreater aspirating force can be applied by a catheter distal inlet portdirectly to the intravascular matter to be aspirated. It is among theobjects of the invention to provide such catheters.

SUMMARY OF THE INVENTION

In accordance with the invention, aspiration catheters are provided inwhich an aspirating force is developed within a small chamber inimmediate proximity to the distal end of the catheter. In someembodiments the catheter has a lumen, at least at its distal end, inwhich a short chamber, in the form of a small distal volume of thelumen, is isolated from more proximal portions of the catheter. A suddenpulse of negative pressure is developed within the small volume. Byconfining the reduced pressure to a small volume at the distal end ofthe catheter, the invention avoids pressure losses that otherwise mayoccur when the suction is developed over the full length of thecatheter. The confined volume of reduced pressure is exposed, suddenly,to the material to be aspirated. The sudden exposure of a clot or otherintravascular matter to the reduced pressure may create a dislodgingforce that also draws the matter into the chamber and is believed tohave increased dislodging force for adherent material, such as thrombusthat may be attached to the vessel wall.

In one embodiment of the invention, the distal end of the catheterincludes a lumen having a distal inlet port and a piston-like elementlocated within the distal end of the lumen close to the inlet port. Inone mode of operation, the piston is slidable longitudinally within thedistal end of the lumen and may be drawn proximally and suddenly by awire or control rod that is connected to the piston and extendsproximally through the catheter to the proximal end of the catheterwhere it can be operated by the clinician. A variable volume chamberthus is defined at the distal end of the catheter by the piston and thewall of the lumen, the distal end of the catheter lumen being open tothe vessel lumen via the inlet port. By drawing the piston proximallyand quickly in the lumen, the volume of the small chamber is increasedrapidly, causing a sudden, momentary reduction in pressure. It isbelieved that the momentary, but sharp, pressure drop created at thedistal end of the catheter lumen will be of sufficient magnitude todislodge and ingest intravascular matter that may not respond to therelatively weaker suction that would be available at the lumen distalend if a source of negative pressure were applied, in the conventionalmanner, at the proximal end of the catheter lumen.

In another embodiment of the invention, the distal chamber includes, atits proximal end, a valved side port in the wall of the catheter thatcommunicates with an aspiration lumen separate from the lumen thatdefines the distal chamber, and which extends to the proximal end of thecatheter. The port is arranged such that it is closed by the pistonuntil the piston has been drawn proximally during its pressure reductionstage sufficiently to expose the side port. The port provides a means bywhich intravascular matter dislodged and ingested into the chamber bythe rapid retraction of the piston then can be aspirated through theport and the aspiration lumen. In this embodiment, the piston can bere-advanced to the distal end of the catheter, closing off the side portand in readiness to effect another cycle of operation.

The embodiment having a separate aspiration lumen may be operated in analternative mode in which the piston seals the side port while negativepressure may be applied from an external source to extensively evacuatethe aspiration lumen, which can serve as a vacuum accumulator within thecatheter body. When the negative pressure has reached a desired level,the piston may be withdrawn to suddenly uncover the side port to exposethe vascular lumen to a sharp, momentary pressure drop to draw thrombusor other intravascular matter into the catheter.

In another embodiment, the piston may be radially expandable andcontractible to operate as a valve that may be selectively opened orclosed. In the expanded configuration, the piston forms a slidable,occlusive seal with the inner surface of the lumen. In the contractedconfiguration, the piston permits flow past the piston. In thisembodiment, the catheter may require only a single aspiration lumen thatcontains the radially expandable piston in the distal end to separatethe proximal portion of the lumen from the distal portion that includesthe distal chamber. As described in one of the embodiments above, bydrawing the piston proximally and quickly in the lumen, the volume ofthe small chamber is increased rapidly, creating a sudden, momentary,strong suction for ingestion of intravascular matter into the chamber.The piston may then be radially contracted to allow conventionalaspiration techniques to draw the matter already taken into the distalchamber proximally past the piston into the proximal portion of theaspiration lumen, and out of the catheter, if so desired. The radiallyexpandable and contractible piston may be left in its expandedconfiguration and operated as a substitute for the non-contractiblepiston in the embodiments described above

In another embodiment, a substantially stationary valving mechanism isprovided to control the exposure of the distal chamber to a suddensuction force. In this embodiment, a piston need not be displaced withinthe aspiration lumen. The radially expandable and contractible pistondescribed above is one means of providing the stationary valvingmechanism. When the piston is expanded to seal against the lumen walland isolates the proximal portion of the lumen from the distal chamberin readiness for subsequent rapid radial collapse of the piston,negative pressure may be applied from an external source to extensivelyevacuate the proximal portion of the aspiration lumen, which can serveas a vacuum accumulator. Upon radial collapse of the piston, thenegative pressure in the aspiration lumen is exposed suddenly to thevessel lumen through the short distal chamber causing forcefulaspiration.

DESCRIPTION OF THE DRAWING

The invention will be appreciated more fully from the following furtherdescription, with reference to the accompanying drawings in which arenot to scale and include exaggerations for clarity, including:

FIG. 1 is a somewhat diagrammatic illustration of an over-the-wirecatheter as may embody the invention;

FIG. 2 is a somewhat diagrammatic illustration of a rapid exchangecatheter that may incorporate the invention;

FIG. 3 is a cross-sectional illustration of the catheter as seen alongthe line 3-3 of FIGS. 1 and 2;

FIG. 4 is a diagrammatic, sectional illustration of the distal end ofone embodiment of the invention in a portion of an artery with thedistal end of the catheter advanced into close proximity to a clot inreadiness to aspirate the clot;

FIG. 5 is a diagrammatic, sectional illustration of the embodiment ofFIG. 4 with the piston withdrawn and with the clot loosened and drawninto the catheter;

FIG. 6 is a diagrammatic, sectional illustration of another embodimentof the invention in which a valved side port and second lumen areassociated with the distal chamber;

FIG. 7 is an illustration of the embodiment as shown in FIG. 6 with theside port valve open to the distal chamber;

FIG. 8 is a diagrammatic illustration of a modification of theembodiment of FIG. 6 in which the piston and side port of the device areconfigured to maintain the side port closed to enable the second lumento function as a vacuum accumulator;

FIG. 9 is an illustration of the modification of FIG. 8 with the pistonwithdrawn to expose the distal chamber to accumulated vacuum;

FIG. 10 is a diagrammatic illustration of an embodiment similar to thatof FIG. 1 but in which the piston is contractible from a radiallyexpanded configuration to a radially contracted configuration, with thepiston in its expanded configuration; and

FIG. 11 is a diagrammatic illustration of the embodiment of FIG. 10 withthe piston in its radially contracted configuration.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Specific embodiments of the present invention are now described withreference to the figures, wherein like reference numbers indicateidentical or functionally similar elements. The terms “distal” and“proximal” are used in the following description with respect to aposition or direction relative to the treating clinician. “Distal” or“distally” are a position distant from or in a direction away from theclinician. “Proximal” and “proximally” are a position near or in adirection toward the clinician.

FIG. 1 illustrates, somewhat diagrammatically, a two-lumen, elongatecatheter 10 having an aspiration lumen 12 and a guidewire lumen 14. Bothlumens may extend substantially the full length of the catheter,although in some embodiments the aspiration lumen may be limited to thedistal region of the catheter. The proximal ends of the lumens mayterminate in a Y-fitting 16, one leg 18 of which receives a guidewire 20and the other leg 22 communicates with the aspiration lumen 12. Thedistal end 24 of the aspiration lumen terminates in a port 25 and may bebeveled, as suggested in FIG. 1 to define a large, oval distal opening.

Catheter 10 may be formed by dual-lumen extrusion. Alternatively, asfurther illustrated in FIG. 3, which is viewed along the line, 3-3 ofFIGS. 1 and 2, for some embodiments, such as the embodiment of rapidexchange catheter 10′, the lumens 12, 14 may be constructed from tubesthat are attached to each other, for example, by a polymeric film 26that is heat shrunk about the tubes. The tube 28 that defines theguidewire lumen 14 may be formed from any of a variety of polymericmaterials commonly used to construct catheters as known to thosefamiliar with the art. As merely one example, lumen 14 may be 0.016 inchin diameter to slidingly receive a 0.014 inch diameter guidewire, as maytypically be used in procedures such as percutaneous transluminalcoronary angioplasty. The tube that defines the aspiration lumen 12 maybe formed as a multilayer structure including an inner lining tube 30,an outer polymeric tube 32 and a reinforcement layer 34 interposedbetween the inner and outer tubes 30, 32. The reinforcement layer 34 maybe a braided tube formed from any of a variety of metals or polymers inaccordance with practices well known to those familiar with the art. Asan example, aspiration lumen 12 may be 0.042 inch in diameter.Reinforced braiding is useful in order to provide kink resistance, toincrease pushability, viz., longitudinal compressive strength, totransmit rotation from the proximal end to the distal end for steeringor directing the catheter tip, and to enhance the resistance of thecatheter to collapse from negative pressures within lumen 12. However, abraiding reinforcement may be omitted if the polymer or other materialselection and catheter wall dimensions are capable of providing therequired physical properties.

FIG. 2 shows another type of aspiration catheter 10′ adapted for use ina “rapid exchange” or “single operator” configuration. In thisembodiment, the catheter has an aspiration tube 36 and a shortenedguidewire tube 38 coupled to the distal portion of the aspiration tube36. The distal portion 40 of the aspiration tube 36 may be formed from apolymeric material while the more proximal portions of the aspirationtube 36 may be formed from hypotubing. Such construction for rapidexchange catheters is well known to those skilled in the art, as shown,for example, in U.S. Pat. No. 5,728,067 (Enger). The distal portion ofthe catheter 10′ may have the same cross-section depicted in FIG. 3, asseen along the line 3-3 of FIG. 2. The guidewire 20 extends through theguidewire tube 38 with most of the guidewire extending proximallyoutside of the catheter shaft.

FIGS. 4 and 5 illustrate, in diagrammatic cross-section, one embodimentof the invention as may be incorporated into a catheter of the typeshown in FIGS. 1-3 except that the aspiration lumen need not extend tothe proximal end of the catheter. FIG. 4 illustrates the distal end ofthe catheter in position to aspirate a clot 48 and FIG. 5 shows thedevice having been operated to ingest the clot 48 through the distalport 25 and into an aspiration chamber 54. FIGS. 4 and 5 show a bloodvessel 42 in which the vessel wall 44 has a stenosis 46 that has becomenarrowed and might present a risk of being obstructed by a clot, showndiagrammatically at 48.

FIG. 4 shows, also diagrammatically, the distal end of an aspirationcatheter, similar to those shown in FIGS. 1 and 2, in which the catheterhas been modified to include a sealing member, such as a piston 50slidably disposed within the distal end of the aspiration lumen 12. Thepiston 50 is connected to a rod 52 that extends from the proximalportion of the piston to the proximal end of the catheter where it canbe manipulated by the clinician. Piston 50 and rod 52 may be formed,alternatively, as an elongate, unitary rod of substantially constantdiameter having a low friction surface and sufficient flexibility topermit sliding movement within aspiration lumen 12, even when catheter10 is disposed in tortuous vascular anatomy. The piston 50 may beconsidered as defining the proximal end of the variable volume chamber54. The length of chamber 54 may range from 1 cm to 15 cm or longer. Asused herein, the term “piston” is intended to refer to any member ordevice that is slidable within the catheter lumen to define, incooperation with the luminal wall and the distal end of the lumen, avariable volume chamber and which maintains a seal with the luminalsurface to cause a pressure drop in the chamber when the piston is movedto expand the volume of the chamber or is otherwise transformed toisolate the chamber 54 from the more proximal portion of the lumen. Thepiston may be in the form of a solid member as shown in FIG. 4 or 5 ormay take other forms, as described further below.

As shown in FIG. 4 the aspiration catheter will have been advanced tothe site of the clot 48 by advancing the catheter over and along apreviously placed guidewire 20. The location of the distal end of thecatheter with respect to the stenosis 46 and clot 48 may be monitoredfluoroscopically to bring the distal end of the catheter in proximity tothe clot 48. When the aspiration catheter is so advanced, the piston 50preferably will be disposed in its most distal position, as suggested inFIG. 4. When the distal end of the catheter is positioned adjacent theclot 48, the rod or wire 52 is pulled to rapidly stroke or displacepiston 50 in a proximal direction, thus quickly expanding the volume ofchamber 54 and thereby developing a, sudden, reduced pressure at thedistal port 25 to ingest the clot into the chamber, as suggesteddiagrammatically in FIG. 5.

It should be understood that the distal chamber 54 is a variable volumechamber in which the volume can be varied, starting from substantiallyzero. The piston 50 may be axially translated from a position where itis fully extended to distal port 25 of the catheter, such that thevolume of chamber 54 is negligible, to a proximal position that createsa greater swept volume. Thus, the distal chamber may be considered asextending from the distal port 25 to the distal face of the piston 50.Thus, suction within the distal chamber 54 can begin to be createdimmediately upon initiating proximal displacement of the piston 50, thusovercoming the delay and loss of suction achieved by conventionalapplication of negative pressure to the proximal end of an aspirationcatheter.

FIGS. 6 and 7 illustrate diagrammatically another embodiment thatoperates in a manner similar to the embodiment of FIGS. 4 and 5 exceptthat a side port 60 is provided in the luminal wall of the aspirationchamber 54. Piston 50 and side port 60 cooperate to provide a valvingmechanism between chamber 54 and another lumen 62, which may extendalongside lumen 12 or surround lumen 12 in a coaxial tube arrangement,as such construction is known to those skilled in the art. The side port60 is positioned so that when the piston 50 has been drawn fullyrearwardly to draw the intravascular matter into the chamber 54, thepiston will expose the side port 60. The side port 60 leads to lumen 62through which the matter may be withdrawn by a conventional aspirationtechnique, as by applying negative pressure to the proximal end of lumen62.

In an alternative mode of operating the embodiment illustrated in FIGS.6 and 7, with piston 50 disposed distally of port 60, negative pressurecan be applied to the proximal end of aspiration lumen 62 such thatlumen 62 and incidentally, lumen 12, can be evacuated to serve as avacuum accumulator or reservoir within the aspiration catheter. Thus,when piston 50 is retracted within lumen 12 to permit communicationbetween chamber 54 and aspiration lumen 62 via port 60, the suddenexposure of the accumulated negative pressure to the vascular lumen,through chamber 54 may forcefully ingest intravascular matter throughthe distal port 25, the side port 60 and possibly into the lumen 62. Inthis mode, it is not the speed or length of the stroke of piston 50 thatare relied on to suddenly generate strong suction at distal port 25.Rather, it is the accumulated negative pressure within lumen 62, whichis immediately available to chamber 54 when port 60 is opened by themovement of piston 50, which acts as a sliding valving mechanism. Forthis reason, port 60 can be located close to distal port 25, if desired,because piston 50 only needs to move the short distance required to openport 60 between lumen 62 and chamber 54. Alternatively, port 60 can belocated farther proximally from distal port 25 such that piston 50 canbe sharply withdrawn to aspirate intravascular matter, as describedabove, and then piston 50 can open to port 60 to apply accumulatedvacuum within lumen 62 to chamber 54. In a modification of thisembodiment (FIGS. 8 and 9), the piston 50′ may be longer than the piston50 of FIGS. 5 and 6 such that the side port 60 can be sealed by thepiston 50′ to prevent incidental evacuation of lumen 12 while lumen 62is accumulating negative pressure.

It may be useful to accumulate a lower pressure in the reservoir thancan be achieved with a single stroke of a syringe, which, for use withaspiration catheters, typically has a volume of 20 cc or larger. Onemeans of accumulating a lower pressure is to connect the proximal end ofaspiration lumen 62 to a central or “wall” vacuum system provided by thehospital or other clinical infrastructure, and which is connected to aremote vacuum pump. Another means of accumulating a lower pressure inthe reservoir is to provide a valve such as a stopcock connected betweenthe proximal end of aspiration lumen 62 and a syringe. The accumulatorcan then be repeatedly evacuated by the syringe, while closing off thestopcock to retain vacuum within the accumulator each time the syringeplunger is reset to zero volume. In this way, the repeated evacuationstrokes of the syringe plunger can be used to “pump down” the pressurein the vacuum accumulator to lower and lower pressures.

FIGS. 10 and 11 illustrate another embodiment in which the sealingmember may comprise a piston 58 defined by a radially expandable andcontractible element. In its expanded, or sealing configuration, thepiston 58 may function as described above, to be suddenly retracted tocreate rapid enlargement of the aspiration chamber 54 at the distal endof the catheter so that a brief, but strong suction can be applied tothe clot to ingest the clot into the chamber. When the piston is in acontracted (FIG. 11) configuration, the aspiration lumen is open fullyfrom the distal port 25 to the proximal end of the catheter, enablingthe already-aspirated material to be drawn proximally beyond the piston58, as by the conventional technique of applying negative pressure tothe proximal end of the lumen. The piston 58 then may be re-expandedinto sealed engagement with the lumen of the catheter and the proceduremay be repeated if desired.

The embodiment of FIGS. 10 and 11 may be operated in an alternate modein which the radially expandable and contractible piston 58 serves as asubstantially stationary valving mechanism. When in a sealingconfiguration, piston 58 seals the distal aspiration chamber 54 from themore proximal portions of the aspiration lumen while the proximalportion of the aspiration lumen may be evacuated by connection to anexternal source of vacuum and maintained at a desired level of negativepressure to function as a vacuum accumulator or suction reservoir, asdescribed above with respect to FIGS. 6-9. When it is desired to performthe aspiration, the piston 58 is contracted radially and suddenly toopen the valving mechanism in the aspiration lumen, thus rapidlylowering the pressure at the distal port 25 in the region of thevascular lumen to be aspirated. Upon aspiration of matter into thecatheter, the matter may be drawn proximally past piston 58 to withinthe proximal portion of the aspiration lumen or out of the catheter, ifdesired. Should another aspiration cycle be desired, the piston 58 maybe re-expanded into sealed engagement with the luminal surface of thecatheter and vacuum may be accumulated again in the proximal portion ofthe aspiration lumen for another cycle.

Alternatively, sealing member 58 may be positioned at the distal tip ofthe aspiration lumen such that the volume of chamber 54 is negligibleand sealing member 58 serves solely a valving function, viz. no slidingpiston function. In this embodiment, with the valving member 58 in itsexpanded, sealed configuration, the entire length of the aspirationlumen may be evacuated to generate a reduced pressure that may beaccumulated until it is desired to perform the aspiration function. Atthat point, the valve element is rapidly collapsed to expose the distalport 25 to a sudden suction pulse to aspirate matter into the catheter.

In this mode of operation, wherein piston 58 serves an expandable andcontractible valving function, it is important that the piston 58 beoperable with rapidity sufficient to rapidly contract its diameter andnot to adversely obstruct flow through the aspiration lumen. To thatend, a direct mechanical mechanism is preferred to expand or contractthe piston 58. It also should be understood that in this mode ofoperation, the piston 58 may not require rapid withdrawal, or anywithdrawal at all, in order to initiate the sudden suction pulse todislodge thrombus or matter. If desired, however, the piston 58 may beoperated in either mode because, when in the expanded configuration,piston 58 may be substituted for either piston 50 or 50′, as describedabove.

The variable profile piston 58 may be formed as a mesh or braidedmaterial in a generally tubular configuration having proximal and distalends 70, 72 that enables the piston to expand when the ends 70, 72 arebrought together and to contract to a low profile when the ends of themesh are urged apart. The mesh may be coated with an appropriatematerial, such as, for example only, a silicone elastomer that providesgood lubricity with the inner surface of the aspiration lumen while alsoproviding a good seal against the surface to facilitate development andretention of suction. The mesh may be expanded by a push-pullarrangement of a tube 74, such as hypotubing and a rod 76 extendingthrough the hypotubing 74. The distal end of the tube 74 may be attachedto the proximal end 70 of the tubular mesh and the distal end of the rod76 may be attached to the distal end 72 of the tubular mesh.Manipulation of the tube and rod effects the change in profile. In otherembodiments, different substantially stationary valving mechanisms maybe located within a distal region of the catheter to serve the samefunction as the radially expandable and contractible piston 58.Exemplary valving mechanisms include a poppet valve and a flapper valve.A poppet valve comprises a disc-shaped head for selectively sealingagainst a ring-shaped seat within the catheter lumen. The position ofthe head is controlled by an elongate stem extending proximally from thehead through the lumen and exiting the catheter. A flapper valve may besimilar to the poppet valve except that the head is hinged on one side,as by a flexible plastic “living” hinge, to swing open and closedagainst the seat.

It should be understood that the foregoing description of the inventionis intended merely to be illustrative thereof and that otherembodiments, modifications and equivalents may be apparent to thoseskilled in the art while remaining within the scope of the invention.

1. A method for aspirating matter from the lumen of a blood vesselcomprising: providing a catheter having a first lumen extending from acatheter proximal end to a distal port open at the distal end of thecatheter and a sealing member slidably disposed within a distal regionof the first lumen and defining a variable volume chamber in the firstlumen between the sealing member and the distal end of the catheter;advancing the catheter intraluminally within the vessel to place thedistal port immediately adjacent matter to be aspirated; withdrawing thesealing member rapidly in the first lumen from a first position to asecond position to increase the volume of the chamber, thus creating asudden reduction in pressure within the variable volume chamber and atthe distal port; whereby the sudden reduction of pressure within thedistal chamber may cause the matter to be aspirated into the variablevolume chamber through the distal port.
 2. The method as defined inclaim 1 wherein, when in the first position, the sealing member islocated fully distally within the first lumen such that an initialvolume of the chamber is substantially negligible.
 3. The method asdefined in claim 1 wherein the sealing member comprises a piston havingan elongate rod extending proximally therefrom through the first lumento exit the proximal end of the catheter and wherein the step ofwithdrawing the sealing member comprises pulling the rod proximallywithin the catheter.
 4. The method as defined in claim 3 wherein thepiston is configured to have an expanded profile configuration in whichit is sealably slidable against the surface of the first lumen and a lowprofile configuration in which it has a reduced profile that enablesflow within the first lumen past the piston.
 5. The method as defined inclaim 4 wherein the piston is expandable and collapsible between itsprofiles by a mechanical push-pull-mechanism operatively connected toproximal and distal ends of the piston.
 6. The method as defined inclaim 3 wherein the piston comprises an expandable and contractibletubular mesh having proximal and distal ends, the mesh having a lowfriction flexible outer impermeable layer adapted to seal against theinner surface of the first lumen.
 7. The method as defined in claim 4wherein the piston further defines a proximal portion of the first lumenextending between the piston and the proximal end of the catheter, themethod further comprising: after aspirating matter into the chamber withthe piston in the expanded profile configuration, contracting the pistonto the low profile configuration to allow the matter to be drawn pastthe piston from the chamber into the proximal portion of the firstlumen.
 8. The method as defined in claim 7 further comprising: applyingnegative pressure to the proximal end of the first lumen to draw thematter proximally past the contracted piston.
 9. The method as definedin claim 7 further comprising: after drawing the matter past the pistoninto the proximal portion of the first lumen, returning the piston tothe first position and transforming the piston from the low profileconfiguration to the expanded profile configuration resealing againstthe surface of the first lumen and repeating the step of withdrawing thesealing member rapidly in the first lumen.
 10. The method as defined inclaim 1 wherein the catheter has a second lumen extending from acatheter proximal end and a side port selectively permitting fluidcommunication between the variable volume chamber and the second lumen,the method further comprising: after aspirating matter into the chamber,opening the side port to allow the matter to be drawn into the secondlumen.
 11. The method as defined in claim 10 wherein the sealing memberopens and closes the side port as it slides across the side port. 12.The method as defined in claim 10 further comprising: applying negativepressure to the proximal end of the second lumen to draw the matterproximally through the open side port.
 13. A catheter for aspiratingmatter from within a blood vessel comprising: an elongate shaft having afirst lumen comprising a variable volume chamber disposed incommunication with a distal port open at the distal end of the catheter;an elongate second lumen extending from the catheter proximal end to aregion of the catheter adjacent the catheter distal end; and a sealingmember slidably disposed within the first lumen to define a moveableproximal end of the variable volume chamber, the sealing member beingadapted to be rapidly withdrawn in the first lumen from a first positionto a second position to increase the volume of the distal chamber, thuscreating a sudden reduction in pressure within the chamber for causingthe matter to be aspirated into the variable volume chamber through thedistal port, the sealing member being further adapted to operate as avalving mechanism to selectively open and close fluid communicationbetween the variable volume chamber and the second lumen.
 14. Thecatheter as defined in claim 13 wherein the second lumen is continuousand coaxial with the first lumen and is separated from the first lumenby the slidable sealing member and wherein the sealing member isconfigured to be selectively transformable between an expanded profileconfiguration sealably slidable against an inner surface of the firstlumen and a low profile configuration having a reduced profile thatenables flow from the first lumen past the piston into the second lumen.15. The catheter as defined in claim 14 wherein the sealing member hasan elongate rod extending proximally therefrom through the second lumenand exiting the proximal end of the catheter to permit a clinician toselectively control the axial position of the sealing member within thecatheter.
 16. The catheter as defined in claim 14 wherein the sealingmember is transformable between its expanded and low profileconfigurations by a mechanical push-pull mechanism operatively connectedto proximal and distal ends of the sealing membrane.
 17. The catheter asdefined in claim 14 wherein the sealing member comprises an expandableand contractible tubular mesh having proximal and distal ends, the meshhaving a low friction flexible outer impermeable layer adapted to sealagainst the inner surface of the first lumen.
 18. The catheter asdefined in claim 13 wherein the first lumen extends from the catheterproximal end to the open distal port and the second lumen is separatefrom the first lumen and in fluid communication with the chamber througha side port formed in the catheter in the proximal region of thevariable volume chamber.
 19. The catheter as defined in claim 18 whereinthe sealing member has an elongate rod extending proximally therefromthrough the first lumen and exiting the proximal end of the catheter topermit a clinician to selectively control the axial position of thesealing member within the catheter.
 20. The catheter as defined in claim18 wherein the sealing member opens and closes the side port as itslides across the side port.
 21. The catheter as defined in claim 13further comprising a source of negative pressure attached to a proximalend of the second lumen.